Motronic 2.8.1 Engine Management System

The Motronic 2.8.1 is an engine management system for V6 engines. It controls both ignition timing and fuel injection from a single control module.

The Motronic system has sequential multiport fuel injection and individual control of ignition timing in connection with knocking in any of the cylinders. This function is adaptive.

Expressed in simplified terms, it could be said that the MOTRONIC system is a combined electronic fuel injection system and electronic ignition system with knock sensor.

The fuel injection system has an advanced function in that injection is sequential. The ignition power module is integrated into the control module.

M2.8.1 control module
Control module 510 monitors and controls a number of functions.

The Control Module Obtains Information from:
^ Mass air flow sensor 205
^ Engine coolant temperature sensor 202
^ Front heated oxygen sensor 136
^ Rear heated oxygen sensor 515
^ Crankshaft position sensor 345
^ Camshaft position sensor 555
^ TTS control module 507
^ Front knock sensor 178
^ Rear knock sensor 178A
^ Throttle position sensor 203
^ A/C status via antifrost thermostat 171
^ Intake air temperature sensor 407
^ Speed sensor 132
^ Transmission range position (automatic transmission) 239

The Control Module Sends Information To:
^ Injectors 206
^ Ignition coil unit 552
^ A/C and ACC relay 156
^ Main relay 229
^ Fuel pump relay 102
^ EDU control module 210
^ Data link connector 348
^ Throttle position sensor 203
^ EVAP canister purge valve 321
^ Idle air control valve (IAC) 272
^ Secondary air injection pump 326
^ Secondary air injection control valve 325
^ Boost pressure control valves for variable intake manifolds 454, 455
^ Engine speed

Power Supply
Current (+30 circuit) is supplied via fuse 23 to pin 18 of the control module. This current is used for the control module's memory.

Current (+15 circuit) is supplied via fuse 13 to pin 27 of the control module. When the ignition switch is turned to the Drive position, main relay 229 is grounded via pin 46 of the control module, causing the relay to operate. The main relay supplies the control module with current (+30 circuit) on pin 37.

Engine Speed
Engine speed data is sent via pin 4 to tachometer 110 in the main instrument display panel and the TTS control module.

Oxygen Sensors 136 And 515
The oxygen sensors, one for the front and one for the rear cylinder block, are mounted on the exhaust pipe. Their task is to give the control module data about the composition of the exhaust gases (oxygen content).

Because the sensors continually measure the oxygen content of the exhaust gases, the control module can correct the fuel-air mixture and bring it as close to lambda = 1 as possible.

Preheating Of Oxygen Sensor 271
To work effectively, the sensor must be warm. The sensors are therefore equipped with an integrated heating element so that they will attain working temperature as quickly as possible. This is known as preheating.

Air Conditioning, A/C
The Motronic control module receives information from the A/C switch/ACC unit as to whether the A/C system is engaged. This information arrives via pressure switch 166 and antifrost thermostat 171.

The control module then grounds relay 155 and the compressor starts. When the compressor is en- gaged, the control module compensates for the increased load on the engine caused by the compressor.

If the engine coolant temperature rises to 11 5°C (239 °F), the EDU control module breaks the connection and the compressor stops.

Coolant Temperature Sensor 202
The coolant temperature sensor is of NTC type and provides the control module with data about the temperature of the coolant.

If there is an open circuit in the sensor, the control module simulates a substitute value.

Throttle Position Sensor 203
The throttle position sensor provides data about the position of the throttle butterfly valve.

The sensor is a potentiometer which provides continuous data from fully closed throttle to wide open throttle.

Idle Air Control Valve 272
The idle air control valve is controlled by the control module, which regulates the opening angle of the butterfly valve in order to maintain the idling speed constant.

For instance, this means that the butterfly valve opens on engagement of the A/C in order to compensate for the increased load on the engine.

Should a fault arise in the circuit, the butterfly valve will be automatically set to a constant idling speed of at least 1000 rpm.

EVAP Canister Purge Valve 321
The EVAP canister purge valve, located in the right- hand side of the engine bay, is controlled by the control module on the basis of engine temperature, engine speed and load.

The valve opens under specific conditions and admits fuel vapours from the evaporative emission canister to the intake manifold where they are burnt with the regular fuel-air mixture.

Crankshaft Position Sensor 345
The control module obtains information on the position and speed of the crankshaft from the crankshaft position sensor.

The sensor consists of a slotted ring on the crankshaft at the flywheel end and an inductive sensor mounted in the engine block. The inductive sensor works rather like a small alternating current generator, the sinusoidal voltage and frequency of which increase with increasing rpm. The sinusoidal voltage alternates between positive and negative polarity, which is achieved by means of teeth on the slotted ring.

This polarity alternation is used by the control module to ascertain the speed of the engine and to identify which cylinder's piston is at or approaching TDC.

If the sensor is not working, the engine will not start.

Camshaft Position Sensor 555
The camshaft position sensor is of the Hall sensor type. It senses the position of the camshaft for cylinder 1 by means of a ridge on the camshaft. When this ridge passes the sensor, the control module input is grounded.

Mass Air Flow Sensor 205
The mass air flow sensor registers the air mass used by the engine, which is proportional to the engine load.

If there is a break in this function, the control module obtains data from the throttle position sensor.

Knock Sensors 178 and 178A
The knock sensors, 178 for the front and 178A for the rear cylinder block, sense the engine's tendency to knock and convert any knocking into a voltage signal. The control module processes the voltage signal and adjusts the ignition timing to achieve optimum performance and minimum emission levels.

Intake air temperature sensor 407
The intake air temperature sensor is located in the intake manifold. It is of NTC type and sends a continuous signal to the control module about the air temperature.
Low temperature = High voltage
High temperature = Low voltage

On the basis of the current air pressure (from manifold absolute pressure sensor 431) and the temperature of the intake air, the current air mass can be determined.

Control Valves 454 And 455
To achieve even and high torque over a wide engine speed range, the engine is equipped with a variable intake manifold.

Using the control valves, which are regulated by the control module, three different pipe lengths can be obtained.

Ignition Coil Module 552
The ignition system is inductive but has no distributer. The module has three ignition coils.

CHECK ENGINE
In the event of a fault in the engine management system or if the emission values are incorrect, the CHECK ENGINE lamp (MIL) in the EDU control module will light up.

Data Link Connector 348
The data link connector for connecting the ISAT scan tool is located under the right-hand front seat.

A direct connection to fuel pump relay 102 has been introduced during the model year.